In order for aircraft seating to be certified for use in an aircraft, the seat must pass a series of performance tests to ensure that it will withstand the various dynamic forces that it may be subjected to, particularly in an emergency situation. In order to be certified as airworthy, aircraft seating designs must pass a series of dynamic tests that simulate aircraft deformation and impulse during emergency conditions. The airworthiness standards for seat structures are described in Federal Aviation Regulation § 25.562, the contents of which is incorporated herein.
Because of the standards set forth in FAR § 25.562, aircraft seating must be strong enough to not only support the weight of the seat occupant, but also to withstand the various load forces that are generated as a result of aircraft maneuvers performed by the pilot during flight, upon landing or, more importantly, in the event of an emergency. These various load forces are known as “g-forces” and result from the forces of acceleration that push or pull on the seat and its occupant when the pilot changes the motion of the aircraft.
G-forces can be positive or negative and can result from either an acceleration or deceleration of the aircraft. Most individuals involved in aviation are familiar with the positive g-forces that result from an aircraft being pulled through a tight radius of turn. In such a turn, the force of the acceleration is increased as greater lift is required to maintain level flight in the turn. This acceleration is a function of the velocity of the aircraft and the radius of the turn and is determined by the equation:a=v2/r where a is the acceleration force, v is the velocity of the aircraft and r is the radius of the turn. This acceleration force a is then divided by g (32 ft/s2) to determine the number of g's resulting from the turn. The number of g's is the multiplier used to determine the weight of an object as a result of the increased acceleration. For example, under a load of 4 g's, an object weighing 10 pounds will feel as though it weighed 40 pounds.
In addition to acceleration loads encountered in flight, g-loads are also experienced during periods of rapid acceleration or deceleration such as occurs during the takeoff and landing phase of a flight. These g-forces which act laterally to the aircraft and its occupants exert a rearward force with respect to the aircraft during periods of acceleration, thereby forcing one back into the seat on takeoff, and a forward force during the period of deceleration on landing, thereby pulling one forward in the seat.
During a normal take-off and landing evolution, a passenger absorbs this g-loading by either pressing back in the seat or leaning forward. In the event of an emergency or crash landing, however, the seat frame itself must be capable of absorbing high g-loads without being deformed or, even worse, snapped out of the floor of the aircraft. This is particularly true of a sideways facing seat such as a divan used in general aviation and business jet type aircraft.
Conventional seats may use a support member extending diagonally between the legs of the seat to brace and strengthen the seat legs. This type of brace does not optimize energy management within the seat, particularly in the case of a divan seat. This is because the straight diagonal brace acts as a static support offering little, if any, dynamic support. For these reasons, a seat frame that was able to provide dynamic support when absorbing high g-forces generated as a result of rapid deceleration encountered in an emergency landing would be an important improvement in the art.